Electric heater



Jan. 22, 1929. v 1,699,898

E. LIGHTFOQT ELE TRIC HEATER Filed July 15, 1927 INVENTOR. Mn. m

ATTORNEYS.

Patented Jan. 22, 1929.

' UNITED STATES 1,699,898 PATENT OFFICE.

EDWIN N. LIGHTFOOT, OF WAUWATOSA, WISCONSIN, ASSIGNOR TO THE CUTLER- HAMMER MFG. CO., OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

ELECTRIC HEATER.

Application filed July 15, 1927. Serial No. 205,987.

This invention relates to electric heaters. More particularly the invention relates to heaters of the type disclosed in United States Letters Patent of C. C. Abbott No. 1,494,939 issued May 20, 1924, this. type of heater comprising a sinuous resistor confined between two metal plates which form heat dissipating vanes for the resistor which preferably is in the form of a helix extend- :0 ing longitudinally of the plates.

' As will be understood, the resistor must be insulated from the enclosing plates whereas it is desirable to afford a maximum degree of heat conductivity from the resistor to the plates and hence the employment in the Abbott heater of a highly refractory powdered insulation compacted to a hard dense mass. The Abbott heater comprises a so-called tubular heater provided with heat 29 dissipating vanes. Y

The present invention has among its objects to provide a similar tubular heater equipped with vanes, but of simpler construction.

A further object of the present invention is to construct such a heater in a manner to avoid the necessity of compacting the insulation about the resistor by externally applied pressure. i Various other objects and advantages of the invention will hereinafter appear.

One embodiment of the invention is illustrated in the accompanying drawing which will now be described, it being understood ea that the embodiment illustrated is susceptible of various modifications without departing from the scope of the appended claims.

In the drawings Fig. 1 is a top plan view of the heater; to partly in section.

Fig. 2 is a side view thereof. Fig. 3 is a sectional view taken on line 3-3 Fig. 1..

Fig. 4 is a sectional viewtaken on line 44 Fig. 1, and

Fig. 5 is a detail view showing a portion of the bottom plate of the heater.

Referring to the drawing, the heater illustrated is of the so-called strip type and comprises a casing formed of two plates. One plate-is a channel plate with lateral flanges, the channel portion being designated by reference character 10v and the flanges by reference character 11. This plate has end flanges 12 which are continuous with the flanges 11 and has at opposite ends of the channel 10 and in communication therewith terminal pockets 13. As will be apparent, this plate may comprise a stamping or may be formed in any other preferred manner. On the other hand, the second plate designated as 14 comprises merely a flat plate having its side and end marginal portions folded over and clamped upon the flanges of the channel plate whereby said plates are fastened together to form a closed casing. Preferably the plate 14 is pressed into intimate contact with the flanges 11 and 12 of the channel plate throughout the extent of such flanges whereby the casing is essentially a tubular casing of relatively small diameter with heat dissipating vanes comprising said flanges and plate 1 The tubular portion of the casing is provided to receive a helical resistor 15 attached to terminals 16 fixed to the channel plate and said terminals having portions within the pockets 13 for attachment thereto of the resistor. Preferably the resistor is in mounting thereof stretched to separate its turns to the desired extent. As will be apparent, the resistor must be mounted in the channel plate prior to assembly of the two plates and it is preferred to introduce the insulation for the resistor after the easing is assembled. Accordingly it is desira ble to provide the resistor with a number of insulating washers. 17 arranged thereon in a spaced relation to center the resistor in the casing during the process of insulating the resistor.

Preferably the insulation comprises magnesium oxide in a powdered or granular state or such material mixed with alundum or other chemically inert insulation in a similar state. Such material may be and preferably is introduced into the :asing after assembly. To this end the plate 14 is provided'with a cut tongue 18 which may be bent outwardly to afford an entrance for the insulation whereas after filling it may be pressed back into position to seal the opening thus afforded.

The tongue 18 is so located as to permit the insulating material to enter one of-the terminal pockets from which it passes to the channel 10 and in practice fillin of the channel may be and preferably is acilitatedand expedited by vibrating the unit.

Assuming use of magnesium oxide or' a distribute the particles of magnesium oxide mixture as that aforementioned the same may be and preferably is subjected to chemical treatment in situ to disintegrate and rethus producing a mass which for practical pur oses isas satisfactory as a magnesium oxi e compacted by externally applied pressure as in swaged tubular heaters. Moreover such chemical treatment may be effected in a simple and convenient manner.

In so treating the magnesium oxide or mixture after the same is introduced into .the casing it is preferred to first wet the material, which can readily be accomplished by forcing or drawing water into the cas ing through the opening afforded by the tongue 18 or through the seams between the plates forming the casing. Also-it is preferred to introduce Water in such quantity as to fill all voids within the casing and then to subject the filling to heat treatment.

A convenient method of thus heat treating the insulating filling is to place the unit in an autoclave, subjecting the filling to the action of steam in the neighborhood of 300 degrees F. or more for a suitable period of time. Under this treatment the magnesium oxide whether used alone or mixed with a pin and'retained thereon by-a washer 21,.

the pin being riveted over said washer. The head of each terminal stud is wrapped with a sheet '22 of mica or other suitable insulating material and each stud carries a mica or other insulating washer 23 to insulate its shank from the casing. Also each stud carries externally of the casing a clamping nut 24: having interposed between the same and the casing an insulating washer 25 of mica or other suitable material and a metal washer 26 immediately beneath the clamping nut. As'will be understood, the terminal fractory insulating material and a casingtherefor having a tubular section to receive said resistor and said insulating material and to confine the latter, said casing having heat dissipating vanes integral with walls of said tubular section and having the walls of said tubular section in direct and intimate'contactwith said mass of insulating material.

2. An electric heater comprising a channel plate with integral flanges extending longitudinally therof, a cover plate for said channel plate which forms therewith a tubular casing with heat dissipating vanes comprising said flanges, granular heat refractory insulation filling said tubular casing and having intimate contact with the walls thereof and a helical resistor embedded in said insulating material.

3. An electric heater comprising an elongated channel plate having integral side flanges and end flanges, a flat cover plate having its edges foldedover said flanges and forming with said channel plate a tubular casing with heat dissipating vanes comprising said flanges, refractory electrical insulating material filling said tubular casing and having intimate contact with the walls of the latter, and a helical resistor embedded in said insulating material.

In witness whereof, I have hereunto subscribed my name.

EDWIN N. LIGHTFOOT. 

